Is it possible that I can force fmod to use just one internal DSP Buffer?
I am doing all the mixing on my own and I want to give the final buffer directly to the sound card. I found that I can squize it down to 2 buffers in setDSPBufferSize. I measured the time between DSP callback calls from fmod and I found that at least 2 buffers will be pulled from my code in less than a full milli second. That brings me to the idea that fmod always needs at least two buffers, but I would need only one.

If setDSPBufferSize is not suitable to do this maybe there is another method to feed the soundcard more directly.

yeah it has a double buffer minimum, that’s just to avoid clicking, because the hardware could be playing from the memory that is being written to. That depends on the output mode though.
There’s no other way to get 1 buffer though.

Well, I got a double buffer as well to prevent clicking 😉 Maybe I shall deactivate this one in favour of yours?
Am I right I can rely that there is at least one double buffer in DirectX, ASIO and CoreAudio? As far as I tested I came up with the conculsion that DX has a double buffer and CoreAudio didn’t not have one. For ASIO I didn’t try indeepth.